1. Field of the Invention
The present invention relates to nitride semiconductor light emitting devices, and more particularly, to a nitride semiconductor light emitting device that improves light emitting efficiency.
2. Description of the Related Art
Recently, group III nitride semiconductors (simply referred to as “nitride semiconductors”) are widely used to manufacture light emitting devices that generate ultraviolet (UV) light, blue light, and green light in various apparatuses such as LCD backlights, camera flashes, and lighting equipment. In general, a nitride semiconductor has a composition represented by equation: AlxGayIn1-x-yN (0≦x≦1, 0≦y≦1, and 0≦x+y≦1). In order to manufacture nitride semiconductor light emitting devices (including LEDs and the like), an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially grown on a growth substrate, such as a sapphire substrate, so as to form a light emitting structure. Here, the active layer may include quantum well layers and quantum barrier layers.
FIG. 1 is an energy band diagram of a nitride semiconductor light emitting device according to the related art. Referring to FIG. 1, a nitride semiconductor light emitting device includes an active layer 12 that has InGaN quantum well layers 12a and GaN quantum barrier layers 12b between an n-type nitride semiconductor layer 11 and a p-type nitride semiconductor layer 13. Here, light is emitted as electrons supplied from the n-type nitride semiconductor layer 11 and holes supplied from the p-type nitride semiconductor 13 are recombined in the active layer 12. In order to improve the recombination of the electrons and the holes in the active layer, there needs to be considerable overlap between a wave function of the electrons and a wave function of the holes. However, a piezoelectric field occurs within the quantum well layers due to a lattice constant mismatch at the interface between the InGaN quantum well layers 12a and the GaN quantum barrier layers 12b. As a result, the overlap between the wave function of the electrons and the wave function of the holes is reduced because the wave function of the electrons and the wave function of the holes become distanced. Therefore, a chronic problem, that is, a decrease in recombination efficiency occurs in the active layer of the nitride semiconductor light emitting device.
In order to solve this, a technique that uses an AlInGaN quantum barrier layer having a similar lattice constant with the InGaN quantum well layers 12a and a similar energy band gap with the quantum barrier layers has been developed. However, when the AlInGaN quantum barrier layer is grown, optimal penetration of Al atoms may be allowed at a temperature of 800° C. or more and a pressure of 199 Torr, and optimal penetration of In atoms may be allowed at a temperature of less than 800° C. and a pressure of approximately 300 Torr. That is, since processing conditions for the optimal penetration of the Al atoms and the In atoms are different from each other, it is difficult to grow an AlInGaN quantum barrier layer having excellent crystalline quality.